cvs commit: src/sys/dev/an if_an.c src/sys/dev/arl if_arl_isa.c src/sys/dev/awi if_awi_pccard.c src/sys/dev/cm if_cm_isa.c src/sys/dev/cnw if_cnw.c src/sys/dev/cp if_cp.c src/sys/dev/cs if_cs.c src/sys/dev/ed if_ed.c src/sys/dev/em if_em.c ...

[Ruslan Ermilov]

On Wed, Sep 21, 2005 at 01:23:22PM -0600, M. Warner Losh wrote:
> In message: <20050921191906.GA24516 at ip.net.ua>
>             Ruslan Ermilov <ru at FreeBSD.org> writes:
> : On Wed, Sep 21, 2005 at 01:02:41PM -0600, M. Warner Losh wrote:
> : > In message: <200509211455.59154.jhb at FreeBSD.org>
> : >             John Baldwin <jhb at FreeBSD.org> writes:
> : > : > 5.  Fix all drivers to set some flag in foo_detach() and foo_shutdown()
> : > : >     and refuse to work in foo_ioctl() if it's set.  This should fix
> : > : >     panics when BPF listener is attached while interface goes away or
> : > : >     module is unloaded.
> : > 
> : > : I'd rather 5) be simpler in 
> : > : that it only check in the flags case to not force the driver lock to be 
> : > : acquired for all the ioctls that the driver doesn't actually handle.  
> : > : Actually, I think I'd really prefer that we think about how to fix the BPF 
> : > : issue in BPF itself if possible.  It may be that we don't need to set the 
> : > : flags (i.e. skip the actual ioctl) if the interface is in the process of 
> : > : detaching and we can make that change centrally without having to scatter 
> : > : gone flags in all the drivers.
> : > 
> : > This would solve the race at hand.  However, it wouldn't solve the
> : > problems with driver shutdown racing with other things in the system
> : > (like ifconfig during detach).
> : > 
> : > I've knocked around the idea of creating a if_dead() function that one
> : > would call before foo_stop().  if_dead would just return (possibly an
> : > error) for all the entry points before the device is actually
> : > detached.  This would mean that we don't need to add flags to all the
> : > drivers, but we do need to change all the detach routine.  This would
> : > avoid the LOCK operations that you are worried about...
> : > 
> : I'm afraid you cannot safely change the ifnet method pointers, if
> : you mean that foo_detach() should set ifp->if_start etc. to point
> : to if_dead().
> 
> Why not?  What's the problem?
> 
The time you change say ifp->if_start in foo_detach(), stack may call
it and get a half-changed pointer.  Unless we invent locking shared
between stack and the drivers.


Cheers,
-- 
Ruslan Ermilov
ru at FreeBSD.org
FreeBSD committer
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